Relatively recently there have been developed various implantable devices for administering infusate such as heparin, insulin and other medicaments over a prolonged term. Examples of such implantable infusion apparatus are disclosed in U.S. Pat Nos. 3,951,147 and 4,193,397.
In many applications of apparatus of this general type, it becomes necessary to change the infusate dosage to the patient on a temporary basis. For example, in the case of an insulin administering device or artificial pancreas, or it is desirable that the patient receive a continuous basal dose of infusate. Then, after a meal when the patient's sugar level rises, a larger or bolus dose of infusate should be administered to counteract the increased sugar level in the patient's blood caused by the ingestion of the food.
This increased dosage may be provided in a variety of ways. For example, in an implantable device such as depicted in the aforementioned U.S. Pat. No. 4,193,397, a single infusate reservoir is provided and infusate is drawn from that reservoir at two different rates to provide the two different dosages. Alternatively, the device may have separate reservoirs containing infusate in different concentrations. Infusate from one or another of these reservoirs is delivered to the infusion site in the patient's body depending upon the circumstances. In either case, however, provision must be made for actuating a valve implanted in the patient's body to establish the two different infusate flows to the infusion site in the patient's body.
Conventionally, such implantable valves are actuated in three different ways. More particularly, as shown in U.S. Pat. No. 4,013,074, a valve can be implanted subcutaneously and provided with a mechanical actuator situated directly under the skin. The valve is opened or closed, as the case may be, by finger pressure on the skin which depresses the actuator. While such a valve may operate satisfactorily, the digital deflection of the patient's skin pinches the skin which may cause valve site tissue damage and discomfort to the patient. Also in some valves of this type, a feedthrough is required in the valve to transmit motion from the valve actuator to the valve interior.
The second type of implantable valve employs a solenoid or piezoelectric crystal to actuate the valve. Finger depression of a subcutaneous button switch connected between the solenoid or crystal and a battery opens and closes the valve. Also, by the use of telemetry, remote actuation of a solenoid or a crystal to open and close the valve can be performed. This type prior valve is disadvantaged in that it requires an implanted battery and ancillary circuitry to provide electrical power to actuate the valve. Such electrical components cannot tolerate autoclaving and the battery must be replaced from time to time necessitating an operation on the patient. Also, as with the first type valve, the skin may be pinched to depress the actuating switch.
The third type of implantable valve is actuated transcutaneously by positioning an external magnet opposite the implanted valve. Such valves are depicted, for example, in U.S. Pat. Nos. 3,315,660 and 3,659,600. A complete magnetically actuated valved infusate pump is disclosed in U.S. Pat. No. 4,152,098. While these prior magnetically actuated devices perform their functions, they do have certain drawbacks which militate against their wider use and application.
More particularly, some prior valves are overly large, particularly in the axial direction which is the direction of valve member movement. Consequently, when implanted under the skin, they penetrate a relatively great distance into body tissue causing patient discomfort. Some valves which are relatively small employ valve member suspension systems which do not flex sufficiently to permit a proper fluid flow rate, or if they do, the components of the suspensions suffer fatigue failure after a relatively short time, requiring valve repair or replacement.
Also some such conventional valves are prone to actuation prematurely upon sudden accelarations of the patient's body as when he jumps up and down or is jostled. Prior attempts to alleviate that problem have resulted in valves having valve member suspension systems which are so stiff that an overly large, unwieldly external actuating magnet is required in order to develop sufficient magnetic force to open or close the valve transcutaneously.
Still further, some prior valves of this third type require slidable valve feedthroughs connected between the valve actuator and the movable valve member. Such sliding or rubbing surfaces are prone to becoming bound up and worn. Also, they generate small particles which can degrade valve operation and become entrained in the infusate being dispensed to the patient, with obvious deleterious consequences.
There are other procedures in which conduits are provided in the body to conduct fluid from one location in the body to another. For example, hydrocephalic shunts are implanted in the body to drain fluid from the cranial cavity to relieve pressure on the brain. Implanted continence devices are also proposed. In all of these devices, it would be desirable to have the option of providing a valve for controlling flow through the conduit that can be actuated extracorporally.